Disc drives are used to store information. The information is stored on discs in the drive along concentric tracks that are often divided into data sectors and servo sectors. The data sectors contain the recorded data and the servo sectors contain information that can be used to position a head for reading and writing along the tracks.
Specifically, servo sectors typically include a preamble that allows the disc drive to generate a demodulation signal for demodulating the remainder of the information in the servo sector; a timing mark that allows the disc drive to establish a starting point for phase computations involving the servo read signal; and a gray code field that can be decoded to identify a track identifier (track ID). The servo sector also contains position error signal (PES) bursts that can be used to determine the position of the head within a track.
In general, there are two types of PES bursts: a null-type and a phase-type. When reading a null-type PES burst, the magnitude of the read signal indicates the position of the head within the track. When reading a phase-type PES burst, the phase of the read signal indicates the position of the head within the track.
Some disc drives utilize patterned media. In patterned media, photolithography and other similar techniques are used to create lands or islands of magnetic material that are surrounded by either non-magnetic material or grooves containing no material.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.